This invention relates to analysers. Embodiments of the invention relate to instruments for the determination of molecular characteristics, such as the length of nucleic acid in terms of base pairs, and the sequencing of genetic samples.
There are several current techniques for analysing materials such as DNA samples in an automated or semi-automated manner. One such technique which has been demonstrated for DNA analysis is the use of so-called microfabricated capillary electrophoresis (CE) chips.
These devices comprise a substrate in which a number of very fine capillary chancels are etched and filled with a gel material. A material to be analysed passes along the capillary channel wider the influence of an electric field. Components of the materialxe2x80x94for example, nucleic acidsxe2x80x94progress along the channel at different rates depending on the relative molecular weights of the components, leading to a separation by molecular weight.
Current techniques use photographic techniques to image radioactive or luminescent tags attached to the nucleic acids. This is a time consuming process. A quicker but expensive alterative is to use phosphor imagers to record the sequences. Furthermore, both processes use hazardous chemicals to tag the nucleic acids and the safe use and disposal of these is a major problem, requiring skilful scientific and technical input.
As mentioned above, all of these techniques are relatively slow. In any current emission technique, such as CE-laser induced fluorescence (CE-UP) the time-to-sequence depends on the separation gradient (i.e. the electric field) and the discriminator power (e.g. the capillary or electrophoresis gel) convolved with the size of the objects to be separated.
There is a need for an improved technique offering a faster response than current techniques and avoiding the use of hazardous materials.
PCT/GB96/01121 discloses an electrophoresis system in which material components are driven along quartz tubes. In effect, the shadow of the separated components is detected by directing an ultraviolet (UV) light from one side of the tubes towards a detector at the other side.
This invention provides analyser comprising: a substrate of diamond, sapphire or a polymer material; an array of one or more elongate capillary channels formed in the substrate; means for driving a sample to be tested along one or more of the channels whereby the velocities of components of the sample along the channels depends on the relative molecular weights of those components; a radiation source and a radiation detector disposed on either side of the channel array so as to detect the presence of material in the channels as interruptions in the radiation path between the radiation source and the radiation detector.
The invention addresses the above problems by providing a new selection of substrates offering many advantages over the glass, quartz and plastics of previous analysers. In particular, the whole apparatus can be miniaturised and the use of hazardous markers is avoided by detecting the xe2x80x9cshadowxe2x80x9d of separated components (e.g. DNA fragments).
Embodiments of the invention can provide an analysis technique which can be carried out while avoiding the use of mutagenic, toxic and carcinogenic chemiluminescent, bioluminescent and radiolabels, with associated benefits in running costs, safety and ease of disposal.
Embodiments of the invention can provide up to an order of magnitude increase in speed for DNA sequencing. For example, a sequence of 500 base pairs which might take 6 hours using a conventional electrophoresis technique could be achieved in 10 minutes using a prototype embodiment of the invention. The saving in time can arise because in current imaging techniques the images of bands identified by conventional labels is heavily smeared by the isotropic emission characteristics of the labels, whereas in embodiments of the present invention the image of a nucleic acid band is substantially the same size as the band, smeared only by diffraction.
Embodiments of the invention can further provide an improved detection sensitivity and signal-to-noise ratio in sub-microlitre sequencing and imaging.
Embodiments of the invention can allow pre-programmed sequence recognition masks to accompany an installation, so that in principle a xe2x80x9cyes-noxe2x80x9d answer could be obtained by relatively untrained end-users. A sequence triage system results which, coupled to the potentially low cost of this technology, could result in the use of apparatus according to embodiments of the invention in doctors"" surgeries, schools and even on individual researchers"" desks.